should / would+ have done sth.
1、 過去將來完成時表示在過去將來某一時間以前發生的動作，並往往會對過去將來某一時間產生影響。 構造：should / would have done sth.
I thought you'd have left by this time.我想這會兒你已經走了。
He told them he would have finished it by 8 o'clock.他告訴他們他會在8點以前幹完。
I guessed that Helen would have told her something.我猜海倫會告訴她一些情況的。
[注]在當代英語中，大家都用 would (縮略式為 'd)